The invention relates to arctic marine transportation systems and, more particularly, to a system for forming a path through a sheet of frozen ice in order to move equipment, such as a marine operations barge, therethrough.
In the past, the principle way in which movement has been managed through frozen arctic waters is by means of ships known as "ice breakers". These ice breakers rely upon the weight of the ship and a reinforced ballast section so that as the engines of the ship drive the bow up onto the surface of the ice the weight of the ship crushes the ice beneath to form a pathway therethrough. Such ice breaking ships are extremely expensive and can only operate in ice fields wherein the ice is no thicker than that for which the ship was designed.
Various proposals, such as that shown in U.S. Pat. No. 2,665,655, have been made for the design of cutting mechanisms which are attached to the front of a ship and driven by power from the ship to saw or grind the ice and form a path therethrough ahead of the ship. Some of the reasons why such systems have not proven practical are that it is very difficult to steer mechanisms powered from the deck of a ship or to cut ice of a thickness often found in the arctic regions without damaging conventional equipment. None of these prior art systems incorporate a floating drum which is driven by a self-contained power source to cut the ice sheet and form a path in advance of a ship.
Many proposals have been made of different techniques for performing marine operations in the arctic regions, such as drilling oil and gas wells, but most of these techniques have proven to be impractical. For example, offshore drilling platforms and equipment located in the arctic ice fields cannot withstand movement of the polar ice pack which is present during much of the arctic year. Similarly, self propelled drilling vessels which are maintained in floating position over a well can be used only during the ice-free portion of the arctic season which is relatively short. In U.S. Pat. No. 3,749,162 to Anders there is disclosed a system for maintaining a drilling barge at a fixed position above a well and floating within a moving pool of water upon the surface of the ice by melting the pool wall in the opposite direction from movement of the ice. Other more exotic approaches such as a drilling barge suspended by air cushions (ground effect operation) above the surface of the ice have also been proposed. Each of these prior art systems possess inherent disadvantages which are overcome by the present method of freezing a drilling barge into place and continuously cutting an annular channel circumferentially around the barge to free it from movement due to that of the surrounding ice sheet.